Computer networks are presently carrying larger and larger volume of information. Both documents and control signals are being sent from one computer to another through computer networks. The control signals are becoming lengthier as one computer tries to control more and more functions of another computer, and documents sent between computers are becoming lengthier. Also the increasing number of people desiring a connection to the network increases the volume handled by the network. Delays in receiving documents and in controlling of the computers increases as the size of the documents, the complexity of the control signals and the number of users on the network increases. Therefore it is very desirable to move data from one network user to another as fast as possible.
One approach to increasing data transfer is to increase the frequency of the network. The length of each bit is therefore decreased and more bits can be transferred in a given time period. However as the frequency increases, components must become more accurate and electrical signals start to behave as electromagnetic waves. These limitations form an upper limit, above which increases in the frequency become uneconomical.
Specifically in LAN applications, there are two well established access methods: Carrier Sense, Multiple Access with Collision Detection (CSMA/CD--ISO/ANSI/IEEE 802.3) and Token (Passing) Ring (802.5 Token Ring). Token Ring further includes a physical ring and physical bus manifestation. These access methods are used with multiple data rates and data formats, generating numerous protocols; in addition, there are other protocols which combine elements of both CSMA/CD and Token Passing, as well as protocols which use only some elements of the access methods (e.g. Carrier Sense, Multiple Access without Collision Detection).
Network concentrators have now been provided with a high speed bus, where all the management and control functions occur in parallel with the actual data packet transfer, and thus incur little or no bandwidth overhead for the management and control. Such a communication system efficiently transfers data as fast as possible without slowing down the system by having to transmit management and control signals in between the transmission of the actual data.
With such a high speed backplane a plurality of dedicated lines (communication paths) are strictly reserved for the transfer of data. Such a high speed backplane bus may include data signal lines, status signal lines, a retry signal line, a busy line, a plurality of slot select lines, a slot select acknowledgement line, a port not ready line, a port ready line, an election synchronization line and an arbiter active line. By each of the modules of a concentrator being able to communicate with all other modules of a concentrator over these lines, the modules are able to elect an arbiter who will individually select which module is to transmit. Then that active arbiter is able to select each of the modules in a uniform manner for transmission onto the datalines. This is all done without having to have large gaps in between actual data transmission, and without each module having to monitor a line to determine if it a collision has taken place. In this way the backplane bus, especially its bandwidth, is used in a most efficient manner without the drawbacks of collisions, a single module dominating the backplane or the existence of large gaps between actual useful data transmissions.
When a module is an active arbiter, it places a signal on the arbiter active line noting to other modules that the arbiter function is being provided by one of the modules. If for any reason an active arbiter can no longer function, the signal is removed from the arbiter active line. When a module notices that a signal is missing from an arbiter active line, or a module desires a new election for active arbiter, the module will place a signal on the election synchronization line and an election process is initiated. The active arbiter then issues the arbiter active signal and begins to select modules for transmitting onto the backplane in a "round robin" manner.
Backplane buses with such high speed modules function quite well with current modules. However, even with current modules, there can be the need to assign one module more of the high speed bus bandwidth than another. Further, newer modules require increasingly more bandwidth.
Newer modules require up to about 200 megabit/second bandwidth. Future modules may require much more bandwidth, for example as much as one gigabit/second bandwidth. The use of a round robin arbitration scheme, that gives each module equal priority for the high speed bus access, is necessarily problematic.